<?php namespace Zmsun\Http\Header;class Etag implements IHeader{public static function fromString($headerLine){$header=new static();list($name,$value)=GenericHeader::splitHeaderLine($headerLine);if(strtolower($name)!=='etag'){throw new \InvalidArgumentException('Invalid header line for Etag string: "'.$name.'"');}$header->value=$value;return$header;}public function getFieldName(){return'Etag';}public function getFieldValue(){return$this->value;}public function toString(){return'Etag: '.$this->getFieldValue();}}